1. Field of the Invention
The present invention relates to a silicone polymer, and, more particularly, to a silicone polymer swelling in silicone oil, a paste-like silicone composition comprised of said silicone polymer which is a stable and homogeneous water-in-oil type, and a cosmetic composition comprising said paste-like silicone composition.
2. Description of the Background Art
Silicone oils are used as a base oil for a number of compositions in a wide variety of fields, including medical products, cosmetics, and the like, because of their safety. In recent years, low viscosity silicone oils, particularly those having viscosities of 100 cS or lower, are attracting the attention due to their superior spreadability, excellent freshness, and high safety. Their applications to various compositions are under study.
A large amount of a viscosity-increasing agent must be added for the preparation of a paste-like or greasy silicone composition using such a low viscosity silicone oil as a base oil. The addition of a large amount of a viscosity-increasing agent, however, makes it difficult to obtain a smooth and homogeneous composition and produces a composition with a poor stability due to separation or issue of the low viscosity silicone oil from the composition.
In order to avoid this problem, many types of viscosity increasing agents to be used for low viscosity silicone oils have been proposed, including organic materials, e.g., fatty acid esters of dextrin (Japanese Patent Laid-open (ko-kai) Nos. 121764/1987, 143970/1987, 143971/1987, and 159489/1988), fatty acid esters of sucrose (Japanese Patent Laid-open (ko-kai) No. 235366/1988), trimethyl-silylated polyvinyl alcohols or trimethyl-silylated polysaccharides (Japanese Patent Laid-open (ko-kai) No. 240335/1987), cellulose ethers containing fatty acid ester groups (Japanese Patent Laid-open (ko-kai) No. 260955/1988); and inorganic materials, e.g., montmorillonite clays (Japanese Patent Laid-open (ko-kai) Nos. 45656/1987, 54759/1987, and 72779/1988). The use of these organic or inorganic materials as viscosity increasing agents, however, entails a problem of reducing the inherent characteristics of low viscosity silicone oils, such as excellent freshness and high spreadability.
Therefore, a method of producing a homogeneous paste-like composition by treating a specific type of silicone polymer as a viscosity increasing agent and a low viscosity silicone oil under a sharing force was recently proposed (Japanese Patent Laid-open (ko-kai) No. 43263/1990). This method, however, involves a problem in that the composition produced cannot homogeneously disperse water therein when water is added to it, even though it provides an excellent viscosity increasing effect. The use of a surfactant can be considered to ensure homogeneous dispersion of water which is an essential component in many medical or cosmetic compositions. In this case, however, it is difficult to effect stable and homogeneous dispersion of water into silicone oils. In addition, the use of surfactants is undesirable because many surfactants are irritative to the skin.
A first object of the present invention is therefore to provide a novel silicone polymer which is capable of converting a low viscosity silicone oil into a paste-like or greasy composition.
A second object of the present invention is to provide a novel paste-like silicone composition which is capable of dispersing water stably and homogeneously without using a surfactant.
A third object of the present invention is to provide a water-in-oil type cosmetic composition which imparting a fresh sensation upon use without stickiness and stable for a long period of time, and a water-in-oil type cosmetic composition having a superior water repellency and a capability of excellently retaining the make-up without running; both prepared by incorporating a low viscosity silicone oil in the oil phase in a stable manner.
The present inventors have conducted extensive studies in order to develop a silicone polymer which can produce a homogeneous paste-like composition swelling in silicone oil and capable of dispersing water. As a result, the present inventors have found that a polymer swelling in a silicone oil can be obtained by the addition polymerization of a mixture of an organohydrogenpolysiloxane having a polyoxyalkylene group in its molecule and an organ-opolysiloxane containing an aliphatic unsaturated group in its molecule, or a mixture of an organohydrogenpolysiloxane and a polyoxyalkylene containing an aliphatic unsaturated group (C.sub.m H.sub.2m-1 group) in its molecule, and that this polymer can act as a viscosity increasing agent for silicone oils and, if kneaded under a shearing force together with a silicone oil, can produce a paste-like silicone composition in which water is homogeneously and stably dispersed.
The present inventors have further found that if said mixture is subjected to the addition polymerization in the presence of a silicone oil having a viscosity of 100 cS or lower at 25.degree. C. and/or a polyhydric alcohol, the resulting polymer exhibits even higher swellability in the silicone oil and that, if kneaded under a shearing force together with a silicone oil, this polymer permits water to more stably and homogeneously disperse into a paste-like silicone composition.
The present inventors further undertaken researches concerning the application of the above paste-like silicone composition to cosmetics.